1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
|
package varint
import (
"encoding/binary"
)
// Decode reads the first varint encoded number from the given buffer.
//
// On success, the function returns the varint as an int64, and the number of
// bytes read (0 if there was an error).
func Decode(b []byte) (int64, int) {
if len(b) == 0 {
return 0, 0
}
// 0xxxxxxx 7-bit positive number
if (b[0] & 0x80) == 0 {
return int64(b[0]), 1
}
// 10xxxxxx + 1 byte 14-bit positive number
if (b[0]&0xC0) == 0x80 && len(b) >= 2 {
return int64(b[0]&0x3F)<<8 | int64(b[1]), 2
}
// 110xxxxx + 2 bytes 21-bit positive number
if (b[0]&0xE0) == 0xC0 && len(b) >= 3 {
return int64(b[0]&0x1F)<<16 | int64(b[1])<<8 | int64(b[2]), 3
}
// 1110xxxx + 3 bytes 28-bit positive number
if (b[0]&0xF0) == 0xE0 && len(b) >= 4 {
return int64(b[0]&0xF)<<24 | int64(b[1])<<16 | int64(b[2])<<8 | int64(b[3]), 4
}
// 111100__ + int (32-bit) 32-bit positive number
if (b[0]&0xFC) == 0xF0 && len(b) >= 5 {
return int64(binary.BigEndian.Uint32(b[1:])), 5
}
// 111101__ + long (64-bit) 64-bit number
if (b[0]&0xFC) == 0xF4 && len(b) >= 9 {
return int64(binary.BigEndian.Uint64(b[1:])), 9
}
// 111110__ + varint Negative recursive varint
if b[0]&0xFC == 0xF8 {
if v, n := Decode(b[1:]); n > 0 {
return -v, n + 1
}
return 0, 0
}
// 111111xx Byte-inverted negative two bit number (~xx)
if b[0]&0xFC == 0xFC {
return ^int64(b[0] & 0x03), 1
}
return 0, 0
}
|
